The human immune system has the capacity to produce antibody specificities to an almost endless variety of antigens. By utilizing germline genes and molecular mechanisms for generation of diversity, the immune system possesses the ability to generate infinite diversity. Evaluation of the expression of the B cell repertoire in non-human species has demonstrated a programmed hierarchy of antibody specificities sequentially expressed during the development of fetal and neonatal immune systems. The presence of most autoantibodies has been considered abnormal in accordance with clonal deletion theories. However, certain naturally occurring, self-recognizing antibody specificities (i.e. DNA binding antibodies) are present in fetal life and probably present at low levels throughout adult life. These naturally occurring antibodies may be preserved in the species because they provide protection from foreign or self antigens. Autoantibodies formulating the adult repertoire may be derived from the same or entirely different gemline variable region sequences. Autoimmune disease may arise from extreme stimulation and/or abnormal regulation of these antibodies. Pathogenic autoantibodies might be derived from either the persistant fetal repertoire, the normal adult, or newly emergent autoantibodies derived from entirely different genes. The goal of this research project is to examine and delineate the development from fetus to adult of the "autoimmune" B cell repertoire and compare it to development of the "normal" B cell repertoire. This project uses a limiting dilution culture system of Epstein-Barr virus infected human B cells. The specific aims of these studies are to answer two questions. First, does the human B cell repertoire develop in a programmed hierarchy of clonotype expression? Second, during the ontogeny of the B cell repertoire are certain V region gene families preferentially used for normal antibody or auto-antibody production? In order to answer the former question we will define at what point(s) in the development of the immune system do anti-DNA, anti- phosphorylcholine (PC) and anti-myoglobin antibody producing clonotypes develop, determine if there exists a preferential site selection for clonotype development, and analyze antibody clonotypes by binding site analysis, isoelectric focusing and idiotype analysis. In order to answer the latter question we will analyze and classify fetal, neonatal, and adult anti-DNA, anti-PC, and anti-myoglobin antibody producing clonotypes by binding site analysis, idiotypic analysis and V region gene family and sequence analysis.